1. Field of the Invention
The present invention generally relates to an apparatus for disruption of cells or viruses using a laser and magnetic beads, and more particularly, to an apparatus capable of effectively detecting DNA by rapidly disrupting cells or viruses using a laser and magnetic beads.
2. Description of the Related Art
Generally, a molecular diagnosis of a specific pathogenic microorganism is performed through the following four steps: 1) cell lysis, 2) DNA isolation, 3) DNA amplification and 4) DNA detection.
The DNA amplification includes a polymerase chain reaction (“PCR”), a ligase chain reaction, a stranded-displacement amplification, a nucleic acid-based amplification, a repair chain reaction, a helicase chain reaction, a Q beta (“QB”) replicase amplification and a ligation activated transcription.
A method of isolating DNA from a cell is conducted with materials having a bonding affinity to DNA. Examples of the materials for DNA separation include silica, glass fiber, anion exchange resin and magnetic beads (see Rudi, K. et al., Biotechniqures 22, pp. 506-511, 1977 and Deggerdal, A. et al., Biotechniqures 22, pp. 554-557, 1997).
Cell lysis is conventionally performed by a mechanical, chemical, thermal, electrical, ultrasonic or microwave method (see Michael T. Talyer et al., Anal. Chem. 73, pp. 492-496, 2001).
The chemical method employs lytic agents for disrupting cells to release DNA. An additional treatment of cell extracts with a chaotropic reagent is necessary to denature proteins. The chemical lysis method is disadvantageous in that harsh chemicals are used to disrupt the cells. Since they can interfere with the subsequent PCR, it is necessary to purify the DNA prior to conducting the PCR. The chemical method is labor-intensive and time-consuming, requires expensive consumables and often has a low DNA yield. The thermal method involves repeated cycles of freezing/melting, but cannot often disrupt many structures within cells.
Heating is an alternative method of disrupting cell walls or membranes. One drawback of simple heating is that it causes the degeneration of proteins that can be attached to released DNA. They can also interfere with DNA amplification. A physical method employs a bulky and expensive pressure unit, but is not suitable for an LOC (Lab-on-a-Chip) application.
An ultrasonic treatment is an alternative of the physical method. In general, the ultrasonic treatment is performed in the state that a cell solution or suspension is put in a chamber located in an ultrasonic bath. However, such ultrasonic disruption has many disadvantages in terms of cell lysis. Firstly, a distribution of ultrasonic energy is not uniform. The nonuniform distribution of ultrasonic energy leads to inconsistent results. Secondly, due to the energy divergence in the ultrasonic bath, it often takes several minutes to completely disrupt cells. Lastly, the ultrasonic method generates unpleasant sounds.
A laser has a lot of advantages in view of the disruption of cells and can be readily applied to LOC (see Huaina Li, et al., Anal. Chem. 73, pp. 4625-4631, 2001). U.S. Patent Application Publication No. 2003/96429 A1 discloses a laser-induced cell lysis system. However, when only a laser is used, it is difficult to make an efficient cell lysis. As a result of doing an experiment using E. coli confirmed that low cell lysis efficiency is obtained when irradiated using a laser only. A concentration of DNA measured after irradiating a laser for 150 seconds is 3.77 ng/μl, whereas that of DNA measured after boiling cells at 95° C. for 5 minutes is 6.15 ng/μl. These results suggest that laser energy was not effectively transferred to cells
Further, such conventional laser-induced cell lysis system has several problems in that it requires bulky and expensive units such as a laser generator and a converging lens, thereby increasing the production cost and making it unhandy to carry. In order to overcome the above problems, an attempt has been made to utilize a low-power laser generator. In such a case, however, there also exists a problem in that since a laser irradiation area is too small to fully cover a reaction area of cells or viruses to be subjected to cell lysis, a uniform and efficient cell lysis procedure cannot be performed.